1. Field of the Invention
The present invention generally relates to methods for enhancing the response speed of liquid crystal displays, and more particularly to such methods which employ multiple times of scanning.
2. The Prior Arts
Liquid crystal displays (LCDs) have become the mainstream technology for computer monitors and TVs. However, due to their physical characteristics, the slower response time of the LCDs compared to the conventional cathode-ray-tube typed displays has been a spirited research topic both in the industry and in the academic arena.
Among the approaches of improving LCD's response time, one such approach that is proven to be effective and has been put into practical use is the one that employs overdriving with double frame rate. For this approach, assuming a pixel (P) has a target voltage level (code 30) in frame (N−1) for the desired grey scale level and a target voltage level (code 120) in frame N, the data driver for the pixel (P) would first apply a larger, overdriving voltage (code 200) in the first half of the frame time of frame (N) and, then in the second half of the frame time, apply the same driving voltage as the target voltage level (code 120). As such, the trajectory of voltage variation of the pixel (P) would reach the target voltage level much faster than when the pixel (P) is applied with the target voltage level (code 120) during the entire frame time. A faster response time is thereby achieved without the penalty of excessive overdriving.
FIG. 1 is a schematic diagram showing the scanning performed by the conventional approach of overdriving with double frame rate. As illustrated, in order to apply two driving voltages to pixels within a single frame time, the approach doubles the frame scanning frequency from the standard 60 Hz to 120 Hz (therefore, referred to as “double frame rate”), which means that the approach scans the entire frame twice within the standard 1/60 sec. frame time. As shown, for the first pass of scanning, the LCD's gate drivers 10 enable the scan lines sequentially from top to bottom and the trajectory of scan line enablement is depicted as the arrow line (1). During the first pass of scanning, the data drivers 20 apply overdriving voltages to the pixels on the enabled scan lines. When the bottommost scan line is enabled in the first pass, the scanning retraces to the top of the LCD screen (shown as the dashed line (12)) and starts the second pass of scanning whose trajectory is depicted as the arrow line (2). During the second pass of scanning, the data drivers 20 apply the target voltage level to the pixels.
Despite of its proven effectiveness in enhancing the LCD's response time, the foregoing approach still has rooms for further improvement. Using any pixel in FIG. 1 as example, after it has been applied with the overdriving voltage, the pixel has to wait an entire frame being scanned before it is applied with the target voltage level in the second pass. In other words, it would take at least 1/120 sec. before the pixel's voltage level approaching the target voltage level.
Another similar approach for enhancing the LCD's response time is to generate an entire black frame during the first pass (whose scan line enablement trajectory is as line (1) of FIG. 1) and then apply the target voltage levels to the pixels during the second pass (whose scan line enablement trajectory is as line (2) of FIG. 1). A variation of this approach is to apply the target voltage levels to the pixels during the first pass and then generate an entire black frame during the second pass. These “black insertion” methods would still suffer the disadvantage that it would need at least 1/120 sec. for pixels to approach their target voltage levels.